1. Field of the Invention
The present invention relates to a hemming apparatus and a hemming process for bending a work such as a metal plate.
2. Description of the Related Art
Various hemming apparatuses which bend a work such as a door panel for automobile have been suggested. As shown in FIG. 8 which illustrates the state before bending of a work, a hemming apparatus 80 possesses an upper mold 81 and a lower mold 82 and a work W is placed between these molds. The upper mold 81 possesses a driver cam 84 having a slant face 84 and a liner 83. The lower mold 84 is composed of a hemming die 89 for fixing the work W that has already been subjected to a previous bending at the processing position WA, a hemming punch 88 for bending the processing position WA of the work W by compressing the position WA, a supporting pole for supporting the hemming punch 88 which can moves vertically, and a slide cam 85 possessing a slant face 85a which is come into contact with the slant face 84a provided via a moving mechanism which holds the supporting pole 87 and which can move horizontally.
Consequently, when the processing position WA of the work W is bent, by descending the upper 81 to bring the slant face 84a of the driver cam into contact with the slant face 85a of the slide cam 85, the slant face 85a is compressed. The slide cam 85 is therefore, pushed toward the work W against the resilient force of the moving mechanism 85 and the hemming punch 88 comes to the processing position WA of the work W. By further descending the upper mold 81, the liner 83 pushes the upper side of the hemming punch 88 to carry out the bending of the processing position WA of the work W.
The apparatus described above is disadvantageous in that the previous bending must be carried out by the use of another apparatus. Consequently, an apparatus as shown in FIG. 7 has been suggested (FIG. 7 illustrates the states after the previous bending and bending). To be specific, a hemming apparatus 90 is comprised of an upper mold 91 and a lower mold 92. The upper mold 91 possesses a driver cam 94 having a slant face 94a and a liner 93, whereas the lower mold 94 possesses a hemming die 99 for providing the work W and for supporting the position WA of the work W, a hemming punch for carrying out previous bending and bending of the processing position WA of the work W, a slide cam 96 for supporting and fixing the hemming punch 95, a revolving cam 95 provided on the backside of the slide cam 95, and a spring 97 which always apply the resilient force to the slide cam 96 in the backside direction.
Consequently, descending the upper mold 91 whereby the slant face 94a pushes the revolving cam 95, the slide cam 96 goes forward against the spring 97 to previously bend the processing position WA of the work W by means of a previous bending slant face 98a of a hemming punch 98. Subsequently, the hemming punch 98 is further pushed to go forward so that the face 98b to be bent placed on the lower side of the hemming punch 98 is positioned at the position where the bending of the processing position WA of the work W has been finished. The bending is carried out by pressing the face 98b by means of the liner 93 from the upper side of the hemming punch 98.
However, the conventional hemming apparatuses have the following problems:
(1) In the case where there coexist linear portions and curved portions at an internal and external circumference portion of the site to be hemmed like window frame of the automobile, it is difficult for the conventional hemming apparatus to carry out bending of the linear portions and curved portions at the narrow position of the work. For this reason, in the conventional hemming apparatus, the bending of the curved portions at the internal circumference portion and the bending of the linear portions at the internal circumference portion are separately carried out. Because of carrying out two separate steps for bending the curved portions and the linear portions, the apparatus should become large as a whole. PA0 (2) Since the hemming conventional apparatuses are separately composed of mounting portions for mounting slide cam and hemming punch, and since they have a large operation by the link mechanism, the rattled portions might be brought about, leading to compression loss and, thus, making it impossible to transmit push compression in an adequate manner. This also results in reduction in the bending precision. PA0 (3) While the conventional hemming apparatuses are required to carry out bending at a compression timing suitable for the conditions of the work, the adjustment of the compression timing, the adjustment thereof is very serious because of complicated construction of the slide cam and other related parts. Moreover, the conventional hemming apparatuses have a large number of parts to be adjusted and, thus, the maintenance of the apparatus is very terrible. PA0 (4) In the case where there are positions to be bent both at the external and internal circumference portions of the work, it is difficult for the conventional hemming apparatuses to secure the space for bending the internal circumference side of the work, making it difficult to design and manufacture the apparatus. PA0 (5) In the case where there are positions to be bent both at the external and internal circumference portions of the work, the conventional hemming apparatuses cannot carry out the bending of the external circumference portion and that of the internal circumference portion at one step. Consequently, the balance between the compressions applied to the external and internal circumference portions of the work is not good and, thus, the deformation of the work might occur.